Curable perfluoropolyether compositions and rubber or gel articles comprising the same

ABSTRACT

Perfluoropolyether compositions are provided comprising (A) a linear perfluoropolyether compound containing at least two alkenyl groups, having a perfluoropolyether structure comprising recurring units —C a F 2a O— in its backbone, and having a Mw of 10,000-100,000; (B) an organosilicon compound containing at least two silicon atom-bonded hydrogen atoms; (C) a reinforcing filler; (D) a hydrosilylation catalyst; and (E) a polyfluoromonoalkenyl compound containing one alkenyl group and having a perfluoropolyether structure in its backbone. The compositions cure into rubber or gel products having improved acid resistance.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2004-174777 filed in Japan on Jun. 11, 2004,the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to perfluoropolyether compositions which cureinto rubber or gel products having heat resistance, oil resistance,chemical resistance, solvent resistance, low-temperature properties,moisture resistance, and low gas permeability and especially, improvedacid resistance. The invention also relates to rubber or gel articlesobtained by curing the compositions.

BACKGROUND ART

Japanese Patent No. 2,990,646 (JP-A 8-199070) discloses a curablecomposition comprising a linear perfluoropolyether compound containingat least two alkenyl groups per molecule and having a perfluoropolyetherstructure in its backbone, an organosilicon compound having at least twoH—SiOSiO structures per molecule, and a hydrosilylation catalyst, whichcures into a product having a good profile of heat resistance, chemicalresistance, solvent resistance, water repellency, oil repellency andweatherability.

These perfluoropolyether rubber compositions perform well in mostapplications. However, their acid resistance is short in thoseapplications requiring chemical resistance such as sealants insemiconductor manufacturing units, sealants and potting materials foruse with engine oil, and sealants and potting materials for use inengine exhaust parts. There is a need for perfluoropolyether rubber orgel compositions which are improved in oil resistance and chemicalresistance, and especially acid resistance.

JP-A 2000-248166 discloses a curable fluoropolyether base rubbercomposition comprising a linear fluoropolyether compound having at leasttwo alkenyl groups, an organosilicon compound having at least two SiHgroups, a hydrosilylation catalyst, and surface-hydrophobicizedmicroparticulate silica having a specific surface area of at least 50m²/g and a nitrogen atom content of 500-5,000 ppm.

SUMMARY OF THE INVENTION

An object of the invention is to provide curable perfluoropolyethercompositions which are cured into rubber or gel having exhibit good heatresistance, solvent resistance, chemical resistance, weatherability,water repellency and oil repellency and especially acid resistance.Another object is to provide rubber or gel articles comprising the same.

It has been found that perfluoropolyether compositions which cure intorubber or gel products having improved acid resistance are obtainableusing a linear perfluoropolyether compound having a weight averagemolecular weight of 10,000 to 100,000.

In one aspect, the present invention provides a curableperfluoropolyether composition comprising (A) a linearperfluoropolyether compound containing at least two alkenyl groups permolecule, having a perfluoropolyether structure comprising recurringunits —C_(a)F_(2a)O— wherein a is an integer of 1 to 6 in its backbone,and having a weight average molecular weight of 10,000 to 100,000; (B)an organosilicon compound containing at least two silicon atom-bondedhydrogen atoms per molecule, selected from the class consisting of (B-1)a cyclic organohydrogenpolysiloxane containing at least oneperfluoroalkyl group or perfluoropolyether substituent group permolecule, and (B-2) an organosilicon compound containing at least oneperfluoroalkyl group or perfluoropolyether substituent group permolecule wherein all silicon atom-bonded hydrogen atoms formH—Si(CH₂)_(g)Si— structures wherein g is an integer of 1 to 3; (C) areinforcing filler; and (D) a hydrosilylation catalyst, the compositionbeing cured into a rubber.

In another aspect, the present invention provides a curableperfluoropolyether composition comprising (A) a linearperfluoropolyether compound as defined above; (B) an organosiliconcompound as defined above; (D) a hydrosilylation catalyst; and (E) apolyfluoromonoalkenyl compound containing one alkenyl group per moleculeand having a perfluoropolyether structure in its backbone, thecomposition being cured into a gel.

In this specification, a rubber-like cured product or rubber means acured product which is able to measure hardness according to JIS K 6253or ISO 1619 and especially has a hardness of 10 to 80 according to JISA-type hardness tester or Type A Durometer. On the other hand, gel-likecured product or gel means that a cured product which is unable tomeasure hardness according to JIS A-type hardness tester or Type ADurometer and has a penetration of 1 to 200, especially 10 to 150according to JIS K 2220 or ASTM D-1403.

The perfluoropolyether compositions of the invention, when cured, impartrubber or gel products having good heat resistance, oil resistance,chemical resistance, solvent resistance, low-temperature properties,moisture resistance and low gas permeability, and especially improvedacid resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are transverse cross-sectional views of electronicpackages under test in Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Component (A) of the curable perfluoropolyether compositions accordingto the invention is a linear perfluoropolyether compound containing atleast two alkenyl groups per molecule, having a perfluoropolyetherstructure, preferably divalent perfluoroalkylether structure, in itsbackbone, and having a weight average molecular weight (Mw) of 10,000 to100,000, as determined by gel permeation chromatography (GPC) relativeto polystyrene standards.

The perfluoroalkyl ether structures include structures comprising aplurality of recurring units —C_(a)F_(2a)O— wherein a is at eachoccurrence an integer of 1 to 6, for example, structures represented bythe general formula (7):(C_(a)F_(2a)O)_(q)   (7)wherein q is an integer of 50 to 600, preferably 50 to 400, morepreferably 50 to 200.

Examples of the recurring units —C_(a)F_(2a)O— are:—CF₂O—, —CF₂CF₂O—, —CF₂CF₂CF₂O—,—CF(CF₃)CF₂O—, —CF₂CF₂CF₂CF₂O—,—CF₂CF₂CF₂CF₂CF₂CF₂O—, and —C(CF₃)₂O—.Of these, —CF₂O—, —CF₂CF₂O—, —CF₂CF₂CF₂O—, and —CF(CF₃)CF₂O— arepreferred. It is understood that the perfluoroalkyl ether structure mayconsist of recurring units —C_(a)F_(2a)O— of one type or recurring unitsof two or more types.

The alkenyl groups in the linear perfluoropolyether compound (A) arepreferably those groups having 2 to 8 carbon atoms, especially 2 to 6carbon atoms, and terminated with a CH₂═CH— structure, for example,vinyl, allyl, propenyl, isopropenyl, butenyl, and hexenyl. Of these,vinyl and allyl are preferred. The alkenyl groups may be attached to thebackbone at both ends either directly or through divalent linkages suchas —CH₂—, —CH₂O— or —Y—NR—CO—. Herein Y is —CH₂— or adimethylphenylsilylene group of the formula (Z):

(inclusive of o-, m- and p-positions), and R is hydrogen, methyl, phenylor allyl. There should be included at least two alkenyl groups permolecule.

Suitable perfluoropolyether compounds (A) include polyfluorodialkenylcompounds of the general formulae (8) and (9).CH₂═CH—(X)_(p)—Rf¹-(X′)_(p)—CH═CH₂   (8)CH₂═CH—(X)_(p)-Q-Rf¹-Q-(X′)_(p)—CH═CH₂   (9)In formulae (8) and (9), X is independently —CH₂—, —CH₂O—, —CH₂OCH₂— or—Y—NR¹—CO— wherein Y is —CH₂— or a dimethylphenylsilylene group of thestructural formula (Z) and R¹ is hydrogen, methyl, phenyl or allyl. X′is —CH₂—, —OCH₂—, —CH₂OCH₂— or —CO—NR²—Y′— wherein Y′ is —CH₂— or adimethylphenylsilylene group of the structural formula (Z′) and R² ishydrogen, methyl, phenyl or allyl. Rf¹ is a divalent perfluoropolyetherstructure, and preferably one of above formula (7); that is, of theformula (C_(a)F_(2a)O)_(q). Q is a divalent hydrocarbon group having 1to 15 carbon atoms which may contain an ether bond, for example, analkylene group or an alkylene group containing an ether bond. The letterp is independently 0 or 1.

(inclusive of o-, m- and p-positions)

(inclusive of o-, m- and p-positions)

The linear perfluoropolyether compound serving as component (A) is mostpreferably a compound of the general formula (1).

Herein, X, X′ and p are as defined above, r is an integer of 2 to 6,each of m and n is an integer of 0 to 600, and the sum of m+n is 50 to600.

The linear perfluoropolyether compound of formula (1) should desirablyhave a weight-average molecular weight (Mw) of 10,000 to 100,000, andmost preferably 10,000 to 50,000. Compounds with Mw of less than 10,000undergo substantial swell in gasoline and other solvents, asdemonstrated by a swell factor of at least 6% in gasoline, failing tomeet the requirements of parts that must be gasoline resistant.Compounds with Mw of more than 100,000 are too viscous to work,detracting from practical utility.

Illustrative examples of the linear perfluoropolyether compound offormula (1) are given below.

Note that each of m and n is an integer of 0 to 200, and the sum of m+nis 50 to 200.

In the practice of the invention, to modify the linearperfluoropolyether compound of formula (1) to the desired weight-averagemolecular weight in accordance with the intended use, the linearperfluoropolyether compound may be previously subjected tohydrosilylation with an organosilicon compound bearing two SiH groups ina molecule by means of an ordinary method and under ordinary conditions.The resulting chain-extended product can be used as component (A).

Component (B) is an organosilicon compound having at least two siliconatom-bonded hydrogen atoms (i.e., SiH groups) in a molecule. Theorganosilicon compound (B) serves as a crosslinking agent and chainextender for component (A). When compatibility with and dispersion incomponent (A) and components (E) and (F) to be described later anduniformity after curing are taken into account, the organosiliconcompound should preferably have at least one monovalent perfluoroalkyl,monovalent perfluorooxyalkyl, divalent perfluoroalkylene or divalentperfluorooxyalkylene group in a molecule.

Preferred component (B) is (B-1) a cyclic organohydrogenpolysiloxanecontaining at least one perfluoroalkyl group or perfluoropolyethersubstituent group per molecule. Of these organohydrogenpolysiloxanecompounds (B-1), those of the general formula (5) are preferred.

Herein Rf³ is a monovalent perfluoroalkyl or perfluoropolyether group,R³ is a monovalent hydrocarbon group of 1 to 20 carbon atoms, R⁴ is adivalent hydrocarbon group of 2 to 20 carbon atoms which may contain anether bond, k is an integer of at least 2, 1 is an integer of 1 to 6,and the sum of k+1 is 3 to 10.

Examples of monovalent perfluoroalkyl or perfluoropolyether groupsrepresented by Rf³ include monovalent perfluoroalkyl groups:C_(b)F_(2b+1)—wherein b is an integer from 1 to 20, and preferably from 2 to 10 andmonovalent perfluorooxyalkyl groups:

wherein n is an integer from 2 to 200, preferably 2 to 100.

R³ is a monovalent hydrocarbon group of 1 to 20 carbon atoms, forexample, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl,isobutyl, tert-butyl, pentyl, hexyl, octyl and decyl; cycloalkyl groupssuch as cyclopentyl, cyclohexyl and cycloheptyl; alkenyl groups such asvinyl, allyl, propenyl, isopropenyl, butenyl and hexenyl; aryl groupssuch as phenyl, tolyl, xylyl and naphthyl; and aralkyl groups such asbenzyl, phenylethyl, phenylpropyl. Of these, those free of aliphaticunsaturation are preferred.

R⁴ is a divalent hydrocarbon group of 2 to 20 carbon atoms which maycontain an ether bond. Such divalent linking groups include alkylenegroups, arylene groups, and combinations thereof, in which may intervenean ether-bonding oxygen atom, an amide bond, a carbonyl bond or thelike, with those of 2 to 12 carbon atoms being preferred. Examples ofsuitable divalent linking groups are:—CH₂CH₂—,—CH₂CH₂CH₂—,—CH₂CH₂CH₂OCH₂—,—CH₂CH₂CH₂—NH—CO—,—CH₂CH₂CH₂—N(Ph)-CO—,—CH₂CH₂CH₂—N(CH₃)—CO—, and—CH₂CH₂CH₂—O—CO—.Note that Ph is phenyl.

Examples of suitable compounds having at least one perfluoroalkyl groupor perfluoropolyether substituent group in a molecule as component (B-1)are given below. They may be used alone or in admixture of two or more,or in admixture with component (B-2) to be described later. Note that Meis methyl and Ph is phenyl.

Component (B) also includes (B-2) an organosilicon compound containingat least one perfluoroalkyl group or perfluoropolyether substituentgroup per molecule wherein all silicon atom-bonded hydrogen atoms formH—Si(CH₂)_(g)Si— structures wherein g is 1 to 3.

Of such component (B-2), organosilicon compounds of the general formula(6) are preferred.

Herein i and j are 0 or 1, and not both i and j are 0; R⁵ is amonovalent hydrocarbon group of 1 to 20 carbon atoms; t is 1, 2 or 3,and u is 0, 1, 2 or 3.

In the case where either one of i and j is 0 and the other is 1, Z ishydrogen, -Q-M or -Q-Rf³, Q is a divalent hydrocarbon group of 1 to 15carbon atoms, such as an alkylene, an arylene, and a group in which analkylene group and an arylene group are combined, which may contain anether bond, Rf³ is a monovalent perfluoroalkyl or perfluorooxyalkylgroup as defined above, and M is a group of formula (i):

wherein R⁶ is a monovalent hydrocarbon group of 1 to 20 carbon atoms,and g is an integer of 1 to 3.

In the case where both i and j are 1, Z is -Q-, -Rf′- or -Q-Rf′-Q-, Q isas defined above, Rf′ is a divalent perfluoroalkylene orperfluorooxyalkylene group, M is a group of the formula (ii) and/or agroup of the formula (iii):

wherein Rf⁴ is monovalent perfluoroalkyl or perfluoropolyether group asin Rf³ and g is 1 to 3, with the proviso that there are present at leasttwo groups of formula (ii) per molecule.

Examples of the divalent perfluoroalkylene or perfluorooxyalkylene grouprepresented by Rf′ include divalent perfluoroalkylene groups of theformula:—C_(c)F_(2c)—wherein c is an integer from 1 to 20, and preferably from 2 to 10, anddivalent perfluorooxyalkylene groups of the formulae:

wherein m+n is an integer of 1 to 200 and r is an integer of 2 to 6 and—(CF₂O)_(m)—(CF₂CF₂O)_(n)—CF₂—wherein each of m and n is an integer from 1 to 50.

Examples of suitable compounds having fluorinated groups (B-2) includethe following compounds. They may be used alone or in admixture of twoor more, or in admixture with component (B-1) described above. Note thatMe is methyl and Ph is phenyl.

Component (B) is generally included in an amount effective for curingcomponents (A) and (E), specifically an amount of supplying preferably0.2 to 2 moles, and more preferably 0.5 to 1.3 moles, of hydrosilyl(SiH) groups per mole of total alkenyl groups on components (A) and (E).Too little hydrosilyl (SiH) groups may lead to an inadequate degree ofcrosslinking or under-cure, whereas too much may cause foaming duringcuring.

Component (C) is a reinforcing filler. It is added to the curableperfluoropolyether rubber composition for the purposes of improvingmechanical strength, thermal stability, weatherability, chemicalresistance or flame retardance, reducing heat shrinkage upon curing, orreducing a coefficient of thermal expansion or a gas permeability of anelastomer resulting from curing. The major purpose is to improvemechanical strength.

Examples of the reinforcing filler (C) include fumed silica, wet silica,ground silica, calcium carbonate, diatomaceous earth, carbon black, andvarious powdered metal oxides excluding alumina. They may have beentreated with surface treating agents. From the mechanical strengthstandpoint, fumed silica is preferred; and from the dispersionstandpoint, fumed silica treated with silane surface treating agents ismost preferred.

Hydrophobic treating agents for dry silica, also known as fumed silica,include silicon compounds having hydrolyzable groups, for example,organochlorosilanes such as dimethyldichlorosilane andtrimethylchlorosilane, silazane compounds such as hexamethyldisilazane,and cyclic silazane compounds such as hexamethylcyclotrisilazane. Interalia, dry silica surface treated with organochlorosilane is preferredfor mechanical strength.

Silica treated to be hydrophobic should preferably have a specificsurface area of at least 50 m²/g in order to improve mechanicalproperties. The specific surface area should be up to 300 m²/g becauseotherwise silica-compounded compositions have too much a viscositybuildup.

For the silica fine powder which has been surface treated with surfacetreating agents for hydrophobization, direct treatment in theparticulate state is preferred. Any commonly known techniques may beemployed for the surface treatment. For example, untreated silica powderis fed along with a treating agent to a closed mechanical mixing unit ora fluidized bed under atmospheric pressure where they are admixedtogether for treatment at room temperature or elevated temperature,optionally in the presence of an inert gas. In some cases, a catalystand water for promoting hydrolysis may be used. Kneading is followed bydrying, leaving the treated silica fine powder. The amount of thetreating agent used may be at least the amount computed from thecoverage area for the treating agent.

Furthermore, the silica filler should preferably have a bulk density of30 to 80 g/l. A silica filler with a bulk density of less than 30 g/lmay provide a composition with a viscosity buildup to interfere withcompounding. A silica filler with a bulk density of more than 80 g/l mayfail to achieve a sufficient reinforcement effect.

The reinforcing filler is preferably added in an amount of 1 to 200parts by weight per 100 parts by weight of component (A). An amount of 1to 60 parts by weight is more preferred for consistent mechanicalproperties. Less than 1 pbw of the filler is too small to be uniformlydispersed in the composition whereas more than 200 pbw is difficult tocompound because of a noticeable viscosity buildup.

It is possible to use component (C) in curable perfluoropolyether gelcompositions as an additive for the purposes of providing reinforcementand thixotropy thereto. An appropriate amount of component (C) added tocurable perfluoropolyether gel compositions is preferably 0 to 20 partsby weight per 100 parts by weight of components (A), (B) and (E)combined. The preferred amount is 0 to 10 parts by weight whenproperties of gel cured products are considered. More than 20 parts byweight of the filler fails to provide elastic properties as gel.

Component (D) is a hydrosilylation catalyst which promotes additionreaction between alkenyl groups in components (A) and (E) and hydrosilylgroups in component (B). The hydrosilylation catalysts are typicallynoble metal compounds which are expensive. Platinum and platinumcompounds are thus used because they are readily available.

Exemplary platinum compounds include chloroplatinic acid, complexes ofchloroplatinic acid with olefins such as ethylene, complexes ofchloroplatinic acid with alcohols and vinylsiloxanes, and metallicplatinum supported on silica, alumina or carbon though not limitedthereto. Known platinum group metal compounds other than the platinumcompounds include rhodium, ruthenium, iridium, and palladium compounds,for example, RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂, Ru₃(CO)₁₂, IrCl(CO)(PPh₃)₂,and Pd(PPh₃)₄ wherein Ph denotes phenyl.

The amount of the hydrosilylation catalyst used may be a catalyticamount, and preferably an amount to give 0.1 to 100 ppm of platinumgroup metal based on the total weight of components (A), (B), (C) and(E).

Component (E) is a polyfluoromonoalkenyl compound containing one alkenylgroup per molecule and having a perfluoropolyether structure in itsbackbone. It is preferably a polyfluoromonoalkenyl compound having thegeneral formula (2):Rf²-(X—)_(p)—CH═CH₂   (2)wherein X′ and p are as defined above, Rf² is a group of the generalformula:F—[CF(CF₃)CF₂O]_(w)—CF(CF₃)—wherein w is an integer of 1 to 500.

Illustrative examples of the polyfluoromonoalkenyl compound havingformula (2) are given below.

Herein m is an integer of 1 to 500.

In the curable perfluoropolyether gel composition, an appropriate amountof the polyfluoromonoalkenyl compound having formula (2) compounded is 1to 300 parts, preferably 50 to 250 parts by weight per 100 parts byweight of component (A) or linear perfluoropolyether dialkenyl compound.

Regardless of whether it is a rubber or gel composition, theperfluoropolyether composition of the invention may further comprise (F)a nonfunctional fluoropolymer having a perfluoropolyether structurecomprising recurring units —C_(a)F_(2a)O— wherein a is as defined above,but free of alkenyl groups. This nonfunctional fluoropolymer is mostpreferably linear.

The linear perfluoropolyether compound, when compounded as component(F), serves to improve chemical resistance, solvent resistance andlow-temperature properties without detracting from physical properties.Particularly when it is compounded in perfluoropolyether rubber and gelcompositions, it is effective for imparting improved low-temperatureproperties, typically lowering the glass transition temperature.

Component (F) is preferably at least one linear perfluoropolyethercompound selected from the class consisting of compounds having thegeneral formula (3):A-O—(CF₂CF₂CF₂O)_(d)-A   (3)wherein A is a group of C_(e)F_(2e+1)—wherein e is 1 to 3, and d is aninteger of 1 to 500, and compounds having the general formula (4):A-O—(CF₂O)_(f)(CF₂CF₂O)_(h)-A   (4)wherein A is as defined above, and f and h each are an integer of 1 to300.

Illustrative examples of component (F) are:CF₃O—(CF₂CF₂CF₂O)_(n)—CF₂CF₃ andCF₃—[(OCF₂CF₂)_(n)(OCF₂)_(m)]—O—CF₃wherein m is an integer of 1 to 200, n is an integer of 1 to 200, andm+n is 1 to 200.

An appropriate amount of component (F) compounded varies whether theperfluoropolyether composition is a rubber or gel composition. In theperfluoropolyether gel composition, the preferred amount of component(F) is 20 to 100 parts by weight per 100 parts by weight of components(A) and (E) combined, i.e., polyfluorodialkenyl compound pluspolyfluoromonoalkenyl compound. In the perfluoropolyether rubbercomposition, the preferred amount of component (F) is 10 to 50 parts byweight per 100 parts by weight of component (A). Component (F) may beone or more of suitable compounds.

In addition to components (A) to (F) described above, the compositionsof the invention may further comprise various additives. Suitablehydrosilylation catalyst regulators include acetylenic alcohols such as1-ethynyl-1-hydroxycyclohexane, 3-methyl-1-butyn-3-ol,3,5-dimethyl-1-hexyn-3-ol, 3-methyl-1-penten-3-ol and phenylbutynol;3-methyl-3-penten-1-yne and 3,5-dimethyl-3-hexen-1-yne;polymethylvinylsiloxane cyclic compounds; and organophosphoruscompounds. The addition of such regulators keeps appropriate curereactivity and shelf stability.

Suitable inorganic fillers include iron oxide, zinc oxide, titaniumoxide, calcium carbonate, magnesium carbonate, zinc carbonate, andcarbon black. The addition of such inorganic fillers adjusts thehardness or mechanical strength of cured products of the compositions.Hollow inorganic fillers or spherical rubbery fillers are also useful.

To impart adhesion, any of well-known tackifiers having epoxy, alkoxy orsimilar groups may be added. Such tackifiers may be used in any desiredamounts as long as they do not interfere with properties of thecompositions or properties of the cured products.

The perfluoropolyether rubber or gel compositions of the invention cureinto satisfactory products having good heat resistance, chemicalresistance, solvent resistance, water repellency, oil repellency andweatherability and especially improved acid resistance and thus findinga variety of applications.

The cured perfluoropolyether rubber can be formed by combining 100 partsby weight of component (A) with an amount of component (B) to provide0.2 to 2.0 moles of hydrosilyl groups per mole of total alkenyl groupsin component (A), 5 to 200 parts by weight of component (C), and anamount of component (D) to provide 0.1 to 100 ppm of platinum relativeto the total weight of components (A), (B) and (C). To the mix, 10 to 50parts by weight of component (F) may be added if desired for reducingthe glass transition temperature.

The cured rubber is formed by any of prior art well-known techniques,for example, by casting the composition into a suitable mold and causingthe composition to cure therein, by coating the composition onto asuitable substrate and curing it thereto, or by lamination. The curingis readily achieved by heating at a temperature of about 60 to about150° C. for about 30 to about 180 minutes.

The cured rubber thus obtained is typically a rubber material having ahardness of 10 to 80 according to JIS K6253, a glass transitiontemperature of up to −60° C., and a gasoline saturation swell factor ofup to 6% at 23° C.

The cured perfluoropolyether gel can be formed by combining 100 parts byweight of component (A) with 1 to 300 parts by weight of component (E),an amount of component (B) to provide 0.2 to 2.0 moles of hydrosilylgroups per mole of total alkenyl groups in components (A) and (E), andan amount of component (D) to provide 0.1 to 100 ppm of platinumrelative to the total weight of components (A), (B) and (E). To the mix,20 to 100 parts by weight of component (F) may be added if desired forreducing the glass transition temperature.

The cured gel is formed by any of prior art well-known techniques, forexample, by casting the composition into a suitable mold and causing thecomposition to cure therein, by coating the composition onto a suitablesubstrate and curing it thereto, or by lamination. The curing is readilyachieved by heating at a temperature of about 60 to about 150° C. forabout 30 to about 180 minutes.

The cured gel thus obtained is typically a gel material having apenetration of 10 to 150 according to the consistency test (using a ¼cone) of JIS K2220 or ASTM D-1403, a glass transition temperature of upto −60° C., and a gasoline saturation swell factor of up to 6% at 23° C.

Rubber or gel articles comprising the cured perfluoropolyether rubber orgel compositions of the invention are suitable for use in a variety ofapplications, for example, automobiles, chemical plants, ink jetprinters, semiconductor manufacturing lines, analytical or scientificinstruments, medical equipment, aircraft, and fuel cells.

Specifically, rubber or gel articles comprising the curedperfluoropolyether rubber or gel compositions of the invention aresuitable for use as rubber parts for automobiles, rubber parts forchemical plants, rubber parts for ink jet printers, rubber parts forsemiconductor manufacturing lines, rubber parts for analytical andscientific instruments, rubber parts for medical equipment, rubber partsfor aircraft, tent coating materials, sealants, molded parts, extrudedparts, coats, copier roll materials, electrical and electronicmoisture-proof coatings, sensor potting materials, fuel cell sealingmaterials, and laminate rubber fabrics.

More specifically, rubber or gel articles comprising the curedcompositions of the invention include, but are not limited to,

rubber parts for automobiles, for example, diaphragms such as fuelregulator diaphragms, pulsation damper diaphragms, oil pressure switchdiaphragms, and EGR diaphragms, valves such as canister valves and powercontrol valves, O-rings such as quick connector O-rings and injectorO-rings, and seals such as oil seals and cylinder head gaskets;

rubber parts for chemical plants, for example, pump diaphragms, valves,O-rings, packings, oil seals, and gaskets;

rubber parts for ink jet printers and semiconductor manufacturing lines,for example, diaphragms, valves, O-rings, packings, and gaskets;

rubber parts for analytical and scientific instruments and medicalequipment, for example, pump diaphragms, O-rings, packings, valves, andjoints;

rubber parts for aircraft, for example, O-rings, face seals, packings,gaskets, diaphragms, and valves in fluid piping for engine oil, jetfuel, hydraulic oil and Skydrol®;

rubber parts for fuel cells, for example, sealants between electrodes,O-rings, face seals, packings, gaskets, diaphragms, and valves inhydrogen, air and coolant water feed pipes;

electric and electronic moisture-proof coating materials and sensorpotting materials for use in, for example, gas pressure sensors,hydraulic pressure sensors, temperature sensors, humidity sensors,rotation sensors, gravity sensors, timing sensors, air flow meters,electronic circuits, semiconductor modules, and various control units.

When the inventive compositions are potted or coated onto substrates toform cured products thereon, it is advantageous to use conventionalprimers in order to improve the bond or adhesion of the inventivecompositions to substrates. The use of primers prevents penetration ofchemicals and solvents from the substrate interface, and improves theacid resistance, chemical resistance and solvent resistance of entireparts.

Use may be made of commercially available primers including a silaneprimer based on a silane coupling agent, anorganohydrogenpolysiloxane-based primer, a synthetic rubber-basedprimer, an acrylic resin-based primer, a urethane resin-based primer,and an epoxy resin-based primer.

The cured products of the inventive compositions preferably have aweight gain of up to 6% when saturated in gasoline at 23° C. If thisweight gain is more than 6%, the cured products may fail to exert theirown performance with a possibility that swelling cause malfunction ofthe associated electric or electronic part or allow leakage from theseal.

The cured products of the inventive compositions also preferably have aweight gain of up to 8% when immersed in conc. sulfuric acid (98%) at23° C. If this weight gain is more than 8%, the cured products may allowleakage from the seal or premature occurrence of corrosion in protectedsubstrates or electric or electronic parts.

EXAMPLE

Examples are given below by way of illustration and not by way oflimitation. Note that all parts (pbw) and % are by weight.

Example 1

A composition was prepared by combining 100 pbw of a polymer havingformula (10) (viscosity 5,600 cSt) with 1.5 pbw of fumed silica AerosilR972 (Aerosil Co., Ltd.). There were further added 0.3 pbw of a 50%toluene solution of ethynyl cyclohexanol, 0.2 pbw of a toluene solutionof chloroplatinic acid-vinylsiloxane complex (platinum metalconcentration 0.5 wt %), and 3.3 pbw of a compound having formula (11),followed by mixing.

The composition was press molded at 150° C. for 10 minutes andpost-cured at 150° C. for 50 minutes, forming a cured product,designated Rubber A. Physical properties of the cured product weremeasured according to JIS K6249. The results are shown in Table 1.

Example 2

A composition was prepared by combining 100 pbw of a polymer havingformula (12) (viscosity 7,500 cSt) with 4 pbw of Aerosil R976 (AerosilCo., Ltd.). There were further added 0.3 pbw of a 50% toluene solutionof ethynyl cyclohexanol, 0.2 pbw of a toluene solution of chloroplatinicacid-vinylsiloxane complex (platinum metal concentration 0.5 wt %), and2.7 pbw of a compound having formula (13), followed by mixing.

The composition was press molded at 150° C. for 10 minutes andpost-cured at 150° C. for 50 minutes, forming a cured product,designated Rubber B. Physical properties of the cured product weremeasured according to JIS K6249. The results are shown in Table 1.

Comparative Example 1

A composition was prepared by combining 100 pbw of a polymer havingformula (14) (viscosity 2,500 cSt) with 4 pbw of Aerosil R976 (AerosilCo., Ltd.). There were further added 0.3 pbw of a 50% toluene solutionof ethynyl cyclohexanol, 0.2 pbw of a toluene solution of chloroplatinicacid-vinylsiloxane complex (platinum metal concentration 0.5 wt %), and9.0 pbw of the compound having formula (11) used in Example 1, followedby mixing.

The composition was press molded at 150° C. for 10 minutes andpost-cured at 150° C. for 50 minutes, forming a cured product,designated Rubber C. Physical properties of the cured product weremeasured according to JIS K6249. The results are shown in Table 1.

Gas and Water Vapor Permeability Tests on Rubber

The cured products of Examples 1 and 2 and Comparative Example 1 weremeasured for permeability of various gases (CO₂, NO₂ and SO₂) and watervapor. The test for gas permeability was conducted at a temperature of30° C. using a gas permeability meter M-C3 by Toyo Seiki Mfg. Co., Ltd.and expressed in unit of x10⁻⁹ cm³(STP).cm/cm².sec.cmHg. The test forwater vapor permeability was conducted at a temperature of 40° C. and arelative humidity of 90% according to JIS Z0208.

Gasoline Immersion Test on Rubber

A sample of the composition was weighed and cured in a glass containerhaving a diameter of 30 mm and a height of 15 mm where it was immersedin gasoline at 23° C. A percent weight change was determined uponsaturation swell at 23° C.

Acid Resistance Test (in Weight Change) on Rubber

A sample of the composition was poured in a test tube having a diameterof 8 mm and a length of 90 mm to a height of 30 mm from the bottom,cured therein, and immersed in an acidic solution having a predeterminedconcentration at 23° C. for 3 days. A percent weight change before andafter the immersion was determined.

Acid Resistance Test (in Physical Change) on Rubber

A sample of the composition was poured in a test tube having a diameterof 8 mm and a length of 90 mm to a height of 30 mm from the bottom,cured therein, and immersed in conc. sulfuric acid at 23° C. for 3 days.Changes of rubber physical properties before and after the immersionwere determined.

The results are shown in Table 1. TABLE 1 Rubber A Rubber B Rubber CRubber D Rubber E Initial Hardness 20 25 35 50 70 physical (Durometer A)properties Tensile strength 1.0 1.2 1.1 9.0 8.0 (MPa) Elongation (%) 290230 150 350 200 Physical Hardness 18 23 29 dissolved dissolvedproperties (Durometer A) after acid Tensile strength 0.9 1.1 0.6dissolved dissolved test (MPa) Elongation (%) 300 240 180 dissolveddissolved Gas CO₂ 39 42 46 290 58 permeability NO₂ 76 80 89 640 110(×10⁻⁹ cm³ · cm/ SO₂ 138 160 196 1250 250 cm² · sec · cmHg) Water vaporpermeability 3 5 9 100 50 (g/cm² · 24 hr) Gasoline swell factor (%) 3 28 260 12 Acid conc. HCl 0.0 0.0 0.0 0.2 0.1 resistance/ conc. HNO₃ 0.10.1 0.1 dissolved 0.2 swell factor (%) conc. H₂SO₄ 3.8 4.5 7.9 dissolveddissolved

Note that in the test following the acid immersion, physical propertiesof Rubber D and Rubber E could not be measured because they weredissolved in sulfuric acid.

Rubber D is a silicone rubber based on dimethylsilicone, available asKE951 from Shin-Etsu Chemical Co., Ltd.

Rubber E is a fluorosilicone rubber based on a copolymer ofdimethylsilicone and trifluoropropyl group-containing silicone,available as FE271 from Shin-Etsu Chemical Co., Ltd.

Example 3

A composition was prepared by combining 65 pbw of a polymer havingformula (12) and 10 pbw of a polymer having formula (15) (viscosity 650cSt) with 25 pbw of a polymer having formula (16), 0.15 pbw of a 50%toluene solution of ethynyl cyclohexanol, 0.015 pbw of an ethanolsolution of chloroplatinic acid-vinylsiloxane complex (platinum metalconcentration 3.0 wt %), and 14.2 pbw of a compound having formula (17),followed by mixing.

The composition was heated at 150° C. for one hour, forming a gelproduct, designated Gel A. The penetration of this gel was measuredaccording to ASTM D-1403 using a ¼ cone. The results are shown in Table2.

Example 4

A composition was prepared by combining 45 pbw of the polymer havingformula (10) and 22 pbw of a polymer having formula (18) (viscosity 1000cSt) with 33 pbw of a polymer having formula (19), 0.15 pbw of a 50%toluene solution of ethynyl cyclohexanol, 0.015 pbw of an ethanolsolution of chloroplatinic acid-vinylsiloxane complex (platinum metalconcentration 3.0 wt %), and 8.5 pbw of a compound having formula (20),followed by mixing.

The composition was heated at 150° C. for one hour, forming a gelproduct, designated Gel B. The penetration of this gel was measuredaccording to ASTM D-1403 using a ¼ cone. The results are shown in Table2.

Comparative Example 2

A composition was prepared by combining 35 pbw of the polymer havingformula (14) and 40 pbw of the polymer having formula (15) (viscosity1000 cSt) with 25 pbw of the polymer having formula (16), 0.15 pbw of a50% toluene solution of ethynyl cyclohexanol, 0.015 pbw of an ethanolsolution of chloroplatinic acid-vinylsiloxane complex (platinum metalconcentration 3.0 wt %), and 13.5 pbw of a compound having formula (21),followed by mixing.

The composition was heated at 150° C. for one hour, forming a gelproduct, designated Gel C. The penetration of this gel was measuredaccording to ASTM D-1403 using a ¼ cone. The results are shown in Table2.

Comparative Example 3

A composition was prepared by combining 40 pbw of the polymer havingformula (10) and 35 pbw of the polymer having formula (15) (viscosity1000 cSt) with 25 pbw of the polymer having formula (16), 0.15 pbw of a50% toluene solution of ethynyl cyclohexanol, 0.015 pbw of an ethanolsolution of chloroplatinic acid-vinylsiloxane complex (platinum metalconcentration 3.0 wt %), and 8.1 pbw of a compound having formula (22),followed by mixing.

The composition was heated at 150° C. for one hour, forming a gelproduct, designated Gel D. The penetration of this gel was measuredaccording to ASTM D-1403 using a ¼ cone. The results are shown in Table2.

Gasoline Immersion Test on Gel

A sample of the composition was weighed and cured in a glass containerhaving a diameter of 30 mm and a height of 15 mm where it was immersedin gasoline at 23° C. A percent weight change was determined uponsaturation swell.

Acid Resistance Test (in Weight Change) on Gel

A sample of the composition was poured in a test tube having a diameterof 8 mm and a length of 90 mm to a height of 30 mm from the bottom,cured therein, and immersed in an acidic solution having a predeterminedconcentration at 23° C. for 3 days. A percent weight change before andafter the immersion was determined.

Acid Resistance Test (in Physical Chance) on Gel

A sample of the composition was poured in a test tube having a diameterof 8 mm and a length of 90 mm to a height of 30 mm from the bottom,cured therein, and immersed in conc. sulfuric acid at 23° C. for 3 days.A change of penetration before and after the immersion were determined.

Acid Resistance Test (in Appearance) on Gel

In the above acid resistance test, after the sample was immersed inconc. sulfuric acid at 23° C. for 3 days, the appearance of the samplewas observed and rated “OK” for no change, “Fair” for a little change orslight turbid, “Poor” for substantial changes or white turbid, and“Reject” when it was dissolved.

The results are shown in Table 2. TABLE 2 Gel A Gel B Gel C Gel D Gel EGel F Penetration Initial 40 72 45 68 65 65 After conc. 38 69 58 60dissolved dissolved H₂SO₄ immersion Gasoline swell factor (%) 2 2 6 3 10300 Acid conc. HCl 0.0 0.0 0.0 0.0 0.2 0.1 resistance/ conc. HNO₃ 0.10.1 0.1 0.1 dissolved 0.3 Swell factor conc. H₂SO₄ 4.2 4.8 10.3 18.5dissolved dissolved (%) Appearance after OK OK Poor Fair Reject Rejectconc. H₂SO₄ immersion

Note that in the penetration test following the acid immersion, physicalproperties of Gel E and Gel F could not be measured because they weredissolved in sulfuric acid.

Gel E is a fluorosilicone gel based on trifluoropropyl group-containingsilicone, available as FE57 from Shin-Etsu Chemical Co., Ltd.

Gel F is a silicone gel based on dimethylsilicone, available as KE1052from Shin-Etsu Chemical Co., Ltd.

Example 5

Acid Resistant Test (Manufacturing Plant)

Using Gels A to D obtained in Examples 3 and 4 and Comparative Examples2 and 3, electronic parts were encapsulated for protection as shown inFIGS. 1 and 2. Illustrated in FIGS. 1 and 2 are a housing 1, acomb-shaped electrode 2, a cavity 3, insert pins or leads 4, a pedestal5, an adhesive 5 a, bonding wires 6, and a protective material 7.

An acid resistance test was conducted on these packages. Specifically,the electronic parts protected with Gels A to D were immersed in aqueoussolutions of sulfuric acid and nitric acid having a concentration of 50%at 60° C. for 500 hours in an open atmosphere. After 500 hours, theouter appearance of the parts was visually observed to inspect anycorrosion. The results are shown in Table 3. TABLE 3 Gel A Gel B Gel CGel D Corrosion Electrode intact intact corroded corroded state Wireintact intact corroded corroded Lead intact intact intact corroded

Japanese Patent Application No. 2004-174777 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A curable perfluoropolyether composition comprising (A) a linearperfluoropolyether compound containing at least two alkenyl groups permolecule, having a perfluoropolyether structure comprising recurringunits —C_(a)F_(2a)O— wherein a is an integer of 1 to 6 in its backbone,and having a weight average molecular weight of 10,000 to 100,000, (B)an organosilicon compound containing at least two silicon atom-bondedhydrogen atoms per molecule, selected from (B-1) and (B-2): (B-1) acyclic organohydrogenpolysiloxane containing at least one perfluoroalkylgroup or perfluoropolyether substituent group per molecule, and (B-2) anorganosilicon compound containing at least one perfluoroalkyl group orperfluoropolyether substituent group per molecule wherein all siliconatom-bonded hydrogen atoms form H—Si(CH₂)_(g)Si— structures wherein g isan integer of 1 to 3, (C) a reinforcing filler, and (D) ahydrosilylation catalyst, said composition being cured into a rubber. 2.The curable perfluoropolyether composition of claim 1, wherein incomponent (A), the perfluoropolyether structure comprising recurringunits —C_(a)F_(2a)O— is represented by (C_(a)F_(2a)O)_(q) wherein q isan integer of 50 to
 600. 3. The curable perfluoropolyether compositionof claim 1, wherein component (A) is a linear perfluoropolyethercompound having the general formula (1):

wherein X is —CH₂—, —CH₂O—, —CH₂OCH₂— or —Y—NR¹—CO— wherein Y is —CH₂—or a dimethylphenylsilylene group of the structural formula (Z):

(inclusive of o-, m- and p-positions), and R¹ is hydrogen, methyl,phenyl or allyl, X′ is —CH₂—, —OCH₂—, —CH₂OCH₂— or —CO—NR²—Y— wherein Yis —CH₂— or a dimethylphenylsilylene group of the structural formula(Z′):

(inclusive of o-, m- and p-positions), and R² is hydrogen, methyl,phenyl or allyl, p is independently 0 or 1, r is an integer of 2 to 6, mand n each are an integer of 0 to 600, the sum of m+n is 50 to
 600. 4.The curable perfluoropolyether composition of claim 1, wherein component(C) is fumed silica which has been treated with a silane surfacetreating agent.
 5. The perfluoropolyether composition of claim 1,further comprising (F) at least one linear polyfluoro compound selectedfrom the class consisting of compounds having the general formula (3):A-O—(CF₂CF₂CF₂O)_(d)-A   (3) wherein A is a group ofC_(e)F_(2e+1)—wherein e is an integer of 1 to 3, and d is an integer of1 to 500, and compounds having the general formula (4):A-O—(CF₂O)_(f)(CF₂CF₂O)_(h)-A   (4) wherein A is as defined above, and fand h each are an integer of 1 to
 300. 6. The perfluoropolyethercomposition of claim 1, having a fluorine content of at least 60%. 7.The perfluoropolyether composition of claim 1, wherein component (B-1)is a cyclic organohydrogenpolysiloxane having the general formula (5):

wherein Rf³ is monovalent perfluoroalkyl or perfluoropolyether group, R³is a monovalent hydrocarbon group of 1 to 20 carbon atoms, R⁴ is adivalent hydrocarbon group of 2 to 20 carbon atoms which may contain anether bond, k is an integer of at least 2, and 1 is an integer of 1 to6.
 8. The perfluoropolyether composition of claim 1, wherein theorganosilicon compound wherein all silicon atom-bonded hydrogen atomsform H—Si(CH₂)_(g)Si— structures (B-2) has the general formula (6):

wherein i and j are 0 or 1, excluding the case where both i and j are 0,in the case where either one of i and j is 0 and the other is 1, Z ishydrogen, -Q-M or -Q-Rf³, Q is a divalent hydrocarbon group of 1 to 15carbon atoms which may contain an ether bond, Rf³ is a monovalentperfluoroalkyl or perfluorooxyalkyl group, M is a group of formula (i):

R⁶ is a monovalent hydrocarbon group of 1 to 20 carbon atoms, and g isan integer of 1 to 3, in the case where both i and j are 1, Z is -Q-,-Rf′- or -Q-Rf′-Q-, Q is as defined above, Rf′ is a divalentperfluoroalkylene or perfluorooxyalkylene group, M is a group of theformula (ii) and/or a group of the formula (iii):

wherein Rf⁴ is monovalent perfluoroalkyl or perfluoropolyether group andQ and g are as defined above, with the proviso that there are present atleast two groups of formula (ii) per molecule, R⁵ is a monovalenthydrocarbon group of 1 to 20 carbon atoms, t is 1, 2 or 3, and u is 0,1, 2 or
 3. 9. The perfluoropolyether composition of claim 1, which curesinto a product having a weight gain of up to 6% when saturated ingasoline at 23° C.
 10. The perfluoropolyether composition of claim 1,which cures into a product having a weight gain of up to 8% whenimmersed in conc. sulfuric acid (98%) at 23° C.
 11. A rubber articlecomprising the curable perfluoropolyether composition of claim 1 in thecured state.
 12. A rubber article comprising the curableperfluoropolyether composition of claim 1 in the cured state, for use inautomobiles, chemical plants, ink jet printers, semiconductormanufacturing lines, analytical or scientific instruments, medicalequipment, aircraft or fuel cells.
 13. A curable perfluoropolyethercomposition comprising (A) a linear perfluoropolyether compoundcontaining at least two alkenyl groups per molecule, having aperfluoropolyether structure comprising recurring units —C_(a)F_(2a)O—wherein a is an integer of 1 to 6 in its backbone, and having a weightaverage molecular weight of 10,000 to 100,000, (B) an organosiliconcompound containing at least two silicon atom-bonded hydrogen atoms permolecule, selected from (B-1) and (B-2): (B-1) a cyclicorganohydrogenpolysiloxane containing at least one perfluoroalkyl groupor perfluoropolyether substituent group per molecule, and (B-2) anorganosilicon compound containing at least one perfluoroalkyl group orperfluoropolyether substituent group per molecule wherein all siliconatom-bonded hydrogen atoms form H—Si(CH₂)_(g)Si— structures wherein g isan integer of 1 to 3, (D) a hydrosilylation catalyst, and (E) apolyfluoromonoalkenyl compound containing one alkenyl group per moleculeand having a perfluoropolyether structure in its backbone, saidcomposition being cured into a gel.
 14. The curable perfluoropolyethercomposition of claim 13, wherein in component (A), theperfluoropolyether structure comprising recurring units —C_(a)F_(2a)O—is represented by (C_(a)F_(2a)O)_(q) wherein q is an integer of 50 to600.
 15. The curable perfluoropolyether composition of claim 13, whereincomponent (A) is a linear perfluoropolyether compound having the generalformula (1):

wherein X is —CH₂—, —CH₂O—, —CH₂OCH₂— or —Y—NR¹—CO— wherein Y is —CH₂—or a dimethylphenylsilylene group of the structural formula (Z):

(inclusive of o-, m- and p-positions), and R¹ is hydrogen, methyl,phenyl or allyl, X′ is —CH₂—, —OCH₂—, —CH₂OCH₂— or —CO—NR²—Y— wherein Yis —CH₂— or a dimethylphenylsilylene group of the structural formula(Z′):

(inclusive of o-, m- and p-positions), and R² is hydrogen, methyl,phenyl or allyl, p is independently 0 or 1, r is an integer of 2 to 6, mand n each are an integer of 0 to 600, the sum of m+n is 50 to
 600. 16.The perfluoropolyether composition of claim 13, wherein component (E) isa polyfluoromonoalkenyl compound having the general formula (2):Rf²-(X′)_(p)—CH═CH₂   (2) wherein X′ and p are as defined above, Rf² isa group of the general formula:F—[CF(CF₃)CF₂O]_(w)—CF(CF₃)— wherein w is an integer of 1 to
 500. 17.The perfluoropolyether composition of claim 13, further comprising (F)at least one linear polyfluoro compound selected from the classconsisting of compounds having the general formula (3):A-O—(CF₂CF₂CF₂O)_(d)-A   (3) wherein A is a group ofC_(e)F_(2e+1)—wherein e is an integer of 1 to 3, and d is an integer of1 to 500, and compounds having the general formula (4):A-O—(CF₂O)_(f)(CF₂CF₂O)_(h)-A   (4) wherein A is as defined above, and fand h each are an integer of 1 to
 300. 18. The perfluoropolyethercomposition of claim 13, having a fluorine content of at least 60%. 19.The perfluoropolyether composition of claim 13, wherein component (B-1)is a cyclic organohydrogenpolysiloxane having the general formula (5):

wherein Rf³ is monovalent perfluoroalkyl or perfluoropolyether group, R³is a monovalent hydrocarbon group of 1 to 20 carbon atoms, R⁴ is adivalent hydrocarbon group of 2 to 20 carbon atoms which may contain anether bond, k is an integer of at least 2, and 1 is an integer of 1 to6.
 20. The perfluoropolyether composition of claim 13, wherein theorganosilicon compound wherein all silicon atom-bonded hydrogen atomsform H—Si(CH₂)_(g)Si— structures (B-2) has the general formula (6):

wherein i and j are 0 or 1, excluding the case where both i and j are 0,in the case where either one of i and j is 0 and the other is 1, Z ishydrogen, -Q-M or -Q-Rf³, Q is a divalent hydrocarbon group OF 1 to 15carbon atoms which may contain an ether bond, Rf³ is a monovalentperfluoroalkyl or perfluorooxyalkyl group, M is a group of formula (i):

R⁶ is a monovalent hydrocarbon group of 1 to 20 carbon atoms, and g isan integer of 1 to 3, in the case where both i and j are 1, Z is -Q-,-Rf′- or -Q-Rf′-Q-, Q is as defined above, Rf′ is a divalentperfluoroalkylene or perfluorooxyalkylene group, M is a group of theformula (ii) and/or a group of the formula (iii):

wherein Rf⁴ is monovalent perfluoroalkyl or perfluoropolyether group andQ and g are as defined above, with the proviso that there are present atleast two groups of formula (ii) per molecule, R⁵ is a monovalenthydrocarbon group of 1 to 20 carbon atoms, t is 1, 2 or 3, and u is 0,1, 2 or
 3. 21. The perfluoropolyether composition of claim 13, whichcures into a product having a weight gain of up to 6% when saturated ingasoline at 23° C.
 22. The perfluoropolyether composition of claim 13,which cures into a product having a weight gain of up to 8% whenimmersed in conc. sulfuric acid (98%) at 23° C.
 23. A gel articlecomprising the curable perfluoropolyether composition of claim 13 in thecured state.
 24. A gel article comprising the curable 1operfluoropolyether composition of claim 13 in the cured state, for usein automobiles, chemical plants, ink jet printers, semiconductormanufacturing lines, analytical or scientific instruments, medicalequipment, aircraft or fuel cells.